Porpoising

[Skyskipper]

Anyone we are in need of your advice. We just bought a 2021 Mountain Aire 40 ft and the dealer over inflated the tires that it cause significant Porpoising so we weighed the coach, set the air pressure according specification but the Porpoising did not go away. On the way home we went to a Spartan recommended Services Center and they check the ride height but seemed unsure what the root problem was. They said the ride height was fine but it was too dangerous to ride fast over bridges. All advise is welcomed.

[Dutch Star Don]

I'm guessing it's the same issue, they've had for the last two years with the Spartan chassis, undersized/under performing front shocks. You should have a few pop up here who changed out their shocks and solved the issue. Adding Koni EVO's solved the issue.

[ThunderRidge]

I find it incredibly hard to believe that since this has been a know problem and also, seemingly a potentially dangerous situation that, Spartan has not made sure this issue has been resolved.

Thankfully, I have never encountered this problem on my 2018 4362 Dutch Star. I have been over bridge approaches in Illinois that would send you off the road if I had the problem encountered by the OP.

This is a brand new coach under warranty. If it’s a shock problem it should be fixed immediately at no cost to you. I would think that there would be a liability issue here for Spartan/Newmar.

[Capt. Bill]

Change the front shocks to Koni & that should correct the problem.

Happy Trails

[RS505]

We replaced the Bilsteins on our leaf sprung solid axle Itasca with FSB’s and the porpoising went from solid terror to nonexistent.

The ride quality went from bouncy to really smooth. It’s a completely different coach now.

The bilsteins only had about 20k on them but maybe they were worn out

[Skyskipper]

What type of RV do you have? What mm size Bilsteins do you replace? We have a MADP with 60mm?

[Dav L]

High tire pressure has no bearing on "porpoising". If anything it would minimize it as the tire high sidewall rigidity would not deflect and add to the problem..

I agree with all of the above - put some Koni's on it.
I have read other new Newmar customers where Newmar has stepped in to assist so it's worth asking / demanding for some help.

Seems the chassis builder was either economizing and/or tuning for low speed compliant drive feel and Newmar accepted that.

["007"]

Seems like other MFG's have the same problem with a Spartan chassis.
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[TUCSONRAIL]

Why is it that Spartan continues to use shocks with not enough compression or rebound dampening? Maybe for a softer ride? ThunderRidge are you on a Freightliner? I know my Freightliner does not have the problem my previous 2 Spartans had.

[ThunderRidge]

Originally Posted by TUCSONRAIL

Why is it that Spartan continues to use shocks with not enough compression or rebound dampening? Maybe for a softer ride? ThunderRidge are you on a Freightliner? I know my Freightliner does not have the problem my previous 2 Spartans had.

Spartan chassis.